This invention is directed to an improved process for the preparation of over-based Group 2A metal sulfonate greases and thickened compositions. Greases and thickened compositions of the present invention are of the heretofore known thixotropic type which comprise a volatile and/or a nonvolatile liquid carrier of solvents such as mineral oil or mineral spirits or equivalent oil medium together with an oil soluble Group 2A metal sulfonate derived from oil soluble higher molecular weight sulfonic acids.
Thixotropic greases are thickened over-based Group 2A sulfonate compositions particularly calcium sulfonate compositions having corrosion inhibiting properties and having utility for a variety of uses such as automobile and truck body undercoatings, lubricants and various other purposes which are known in the art. Such greases are thickened compositions which have gone into quite widespread use either as lubricants or admixed with other ingredients to produce compositions for use in a variety of environments. Generally speaking, these materials are characterized by reasonably good anti-wear properties, reasonably good resistance to mechanical breakdown, salt spray and water corrosion, together with thermal stability at high temperatures.
These greases are normally prepared in either a one step or a two step process. In the two step process, there is initially prepared a Newtonian solution by admixing a normally liquid oil, commonly a mineral oil or a mineral oil and a non-mineral oil volatile organic solvent such as hexene, with a normally liquid sulfonic acid comprising or containing an aliphatic straight or branch chain having at least 12 carbon atoms and having a molecular weight of from about 300 to about 700. These materials are then added to a Group of 2A metal oxide or metal hydroxide (such as calcium oxide or calcium hydroxide) which together with a promoter serves to produce an over-based Group 2A metal sulfonate which commonly has a large degree of overbasing. The resultant mixture is a Newtonian solution containing the over-based metal sulfonate dissolved or dispersed in the mineral oil, which solution is filtered to form a clear solution. The resulting clear Newtonian solution is then subjected to treatment in a second step which involves generally vigorous mixing and heating in the presence of a converting agent which may be water or water soluble alcohols or glycol ethers such as methyl cellosolve (mono-methyl ether of ethylene glycol) or mixtures, of water and such alcohols, or water soluble acids such as acetic acid or propionic acid. The second step results in converting the Newtonian solution to a non-Newtonian dispersed system in the form of a grease or a thickened composition.
The prior art one step process of forming the greases or thickened compositions differs from the two step process in that essentially all of the ingredients are mixed and there is no separately formed or separately formed and recovered Newtonian solution of an over-based metal sulfonate dissolved or dispersed in mineral oil. From an economic viewpoint, the one step process has a definite advantage over the two step process.
However, in carrying out either of these processes, it becomes apparent that grease reproducibility and ability to meet certain specifications has been erratic at best. Commercial products suffer long periods of time when top quality grease is not produced, but rather a more inferior grease is produced, which while suitable for many or even most applications, it not suitable for certain high demand applications.
Consequently, it would be desirable to determine a method for making a consistently high quality grease, having a dropping point in excess of 650.degree. F. It is further desirable that these greases have a penetration values consistent with National Lubricating Grease Institute (NLGI) grades for most such purposes.
It is therefore an object of the present invention to provide a method for the preparation of an over-based metal sulfonate grease having a dropping point of at least 650.degree. F. Other objects will become apparent to those skilled in this art as the description proceeds.